The market for wireless mobile equipment such as mobile phones and pagers continues to expand rapidly. The antenna is built into the cabinet in some types of mobile wireless equipment. One example of such mobile wireless equipment is a mobile phone with a built-in antenna, and an inverted-F antenna is generally the antenna device employed. In mobile phones, an antenna device which can send and receive more than one frequency band is needed due to the increased use of compound terminals.
FIG. 9 shows conventional inverted-F antenna 100 popularly used as a built-in antenna. Inverted-F antenna 100 shown in FIG. 9 consists of base substrate 101, radiating conductive element 102, shorting part 103 for shorting base substrate 101 and radiating conductive element 102, and power feeder 104 for supplying power to the antenna.
However, the above inverted-F antenna 100 has a narrow frequency band, and can only be used at a single frequency. In addition, to broaden the frequency band, the distance between radiating conductive element 102 and base substrate 101 needs to be extended or radiating conductive element 102 itself needs to be enlarged. It is thus extremely difficult to achieve both downsizing and broader bandwidth.